In recent years, attention is being given to a flat panel display that uses an organic light-emitting element. In particular, a display that uses an organic electroluminescence element (organic EL element) has an advantage that low voltage driving can be performed and high-speed response and a wide view angle are obtained, and therefore device application research including material development has been conducted energetically.
The organic EL element is a carrier injection type surface light-emitting device utilizing an emitted light generated at the time of combining an electron and a hole which reach the light-emitting layer. Various emitted light colors are obtained by the selection of organic materials.
In an organic EL display, when three primary colors of red, green and blue (R, G and B) are used as colors of emitted light from respective pixels, full color display is achieved. Currently, in a process for producing an organic EL display panel, peripheral techniques for realizing full color display are under development.
In view of the device characteristics of the current organic EL elements, a vacuum vapor deposition using low-molecular EL materials is practically employed. In particular, in order to realize full color display, a process for selectively patterning respective light emission pixels of R, G and B by vapor deposition using a mask (vapor deposition mask) is employed.
FIG. 8 illustrates a patterning vapor deposition step for the organic EL display by vacuum vapor deposition. A substrate 102 placed in a vacuum chamber (vacuum vapor deposition chamber) includes pixel electrodes 102a formed by patterning in advance. Pixel electrodes on the substrate 102 are aligned with opening portions 103a of a mask 103. A material is vapor-deposited from a vapor deposition source 104 with a state in which the substrate 102 is in close contact with the mask 103, so that an organic thin film (organic compound layer) having a shape corresponding to an opening pattern of the mask 103 is formed on the substrate 102.
When a material for obtaining each emitted light color is to be evaporated for each of R, G, and B color pixels, a mask is exchanged with another mask according to a vapor deposition material. Alternatively a single mask is relatively shifted in position, thereby realizing separate deposition.
When the mask is thickened, a shadow effect becomes larger, so that there is the case where it is difficult to obtain a film formation pattern having a desirable size. In order to obtain a film formation state in which the thickness and the size are desirable for each pixel, it is effective to thin the mask. When a space between the mask and the substrate becomes excessively large, it is likely to cause insertion of the vapor deposition film into the space. When the insertion is significant, there is the case where a fault such as mixture of emitted light colors which is caused by inserting a material for emitting light of a color into another material for emitting light of a different color in an adjacent pixel.
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2005-158571, after the substrate is aligned with the mask, it is necessary to dynamically press the substrate to bring the mask and the substrate into close contact with each other.
However, in the method disclosed by Japanese Patent Application Laid-Open No. 2005-158571, because at a gap caused in a concave portion of the uneven mask, the substrate and the mask cannot be brought into close contact with each other. Therefore, the insertion occurs at the time of vapor deposition.
A method of using a mask made of a magnetic material and bring the mask and the substrate into close contact with each other by a magnetic force is widely employed as a method for obtaining the close contact between the substrate and the mask. However, according to the studies made by the inventors of the present invention, when the mask and the substrate are brought into close contact with each other by using a magnet during a state in which the substrate and the mask which are aligned with each other in advance are in contact with each other, a phenomenon occurs in which the substrate and the mask are rubbed against each other to damage the mask and the substrate. That is, when the substrate and the mask are brought into close contact with each other by using the magnet, a method of suppressing a position displacement between the mask and the substrate at the time of close contact by the magnet is required.